Technical Field
The present disclosure relates to a wavelength conversion device, and more particularly, to a color wheel device.
Description of Related Art
A conventional color wheel with reflective phosphor powder includes a substrate coated with a highly reflective layer, and phosphor powder is coated on the highly reflective layer. The highly reflective layer is configured to forwardly reflect the light generated by exciting the phosphor powder with laser. In general, a metal reflective layer, a dielectric multi-layer reflective film, or a metal/dielectric multi-layer reflective film can be used as the highly reflective layer.
However, the performance of the color wheel with reflective phosphor powder is greatly influenced by the refractive index of the substrate. Therefore, in designing the highly reflective layer, an angle and a wavelength of incident light are often considered. When the reflective structure with multiple dielectric layers is used, the reflective requirements of full incident angles and full wavelength spectrums have to be met, thus greatly increasing the number of dielectric layers. When the film-coating process is complicated, reliability of the films is decreased and the cost is significantly increased. Therefore, the dielectric multi-layer reflective film is often greatly influenced by the conditions of the incident light. Although the metal reflective layer may not need to consider the incident angle, yet the metal reflective layer is easily oxidized and corroded, and thus the stability of the metal reflective layer is poor.
Furthermore, the phosphor powder is mixed with a glue before being coated onto the highly reflective layer, so that photons generated by the phosphor powder enter the highly reflective layer from a colloidal environment having a refractive index of from about 1.4 to about 1.5. The colloidal environment is different from the general ambient environment of which the refractive index is equal to 1. Owing to the Brewster Angle Effect, a portion of the incident light with a large incident angle may be polarized and penetrate the highly reflective layer and be absorbed by the substrate, thus decreasing the light output of the phosphor powder color wheel.